The present invention relates generally to the art of compressing a gas. More particularly, the present invention relates to the compression of a refrigerant gas. Further, the present invention relates to the compression of a refrigerant gas into which a liquid is injected during the compression process. With still more particularlity, the invention relates to the requirement to separate entrained injected oil from the oil-gas mixture discharged by a compressor in a refrigeration circuit. Finally, the invention relates to apparatus for centrifugally separating entrained oil from the mixture of compressed refrigerant gas and atomized oil discharged from a screw compressor in a refrigeration circuit.
Compressors are used in refrigeration circuits to raise the pressure of a refrigerant gas from a suction to a discharge pressure which permits the refrigerant to be used within the circuit to cool a desired medium. Many types of compressors, including rotary screw compressors, are commonly employed to compress the refrigerant gas in a refrigeration circuit. Two complementary rotors, a male and a female, are located in the screw compressor housing. The screw compressor housing has a low pressure end which includes a suction port and a high pressure end which includes a discharge port. Refrigerant gas at suction pressure enters the low pressure end of the compressor housing and is there enveloped in a pocket formed between the turning complementary rotors. The volume of the gas pocket decreases and the pocket is circumferentially displaced as the compressor rotors continue to rotate and mesh. The gas within such a pocket is compressed, and therefore heated, by virtue of the decreasing volume in which it is contained prior to the pocket's opening to the discharge port. The pocket, as it continues to decrease in volume, eventually opens to the discharge port in the high pressure end of the compressor housing and the compressed gas is discharged from the compressor.
Screw compressors used in refrigeration applications will, in the large majority of instances, include an oil injection feature. Oil is injected into the working chamber of the compressor, and therefore into the refrigerant gas being compressed therein for several reasons. First, the injected oil acts to cool the refrigerant gas undergoing compression. As a result, the compressor rotors are cooled allowing for tighter tolerances between the rotors. Second, the oil acts as a lubricant. One of the two rotors in a screw compressor is normally driven by an external source, such as an electric motor, with the other rotor being driven by virtue of its meshing relationship with the externally driven rotor. The injected oil prevents excessive wear between the driving and driven rotors. Finally, oil injected into the working chamber of a screw compressor acts as a sealant between the meshing rotors and between the rotors and the working chamber in which they are contained in the compressor housing. Oil injection therefore increases the efficiency and prolongs the life of a screw compressor.
Oil injected into the working chamber of a screw compressor is atomized and becomes entrained in the refrigerant gas undergoing compression. Such oil, to a great extent, must be removed from the oil-rich mixture discharged from the compressor in order to make the oil available for reinjection into the compressor for the purposes enumerated above. Further, removal of excess injected oil must be accomplished to ensure that the performance of the refrigerant gas is not unduly affected within the refrigeration circuit.
Screw compressors have proven to be particularly suited for use in large capacity refrigeration systems with application in 40 to 400-ton systems being common. The size of such compressors and the amount of oil injected thereinto is significant. Injection of one part oil for every five parts of circulated refrigerant by weight coupled with a requirement to remove 90% or more of the injected oil immediately upon discharge of the mixture from the compressor is typical.
Liquid-gas separators have historically comprised large separator receiver combinations which have included, in many instances, baffle schemes to facilitate liquid-gas separation. Such separator apparatus, as indicated in U.S. Pat. No. 3,917,474 to Heckenkamp et al, are neither simple nor inexpensive to fabricate. Further, many such units call for the separator element to be removable in order to allow for its cleaning or replacement. There exist many applications and environments in which the compressor installation is not readily accessible or in which opening of the compressor apparatus to the environment is undesirable. In such cases the refrigeration equipment, including the liquid separator apparatus, is preferably hermetically or semi-hermetically sealed. Provision must therefore be made for liquid separator apparatus which is highly reliable yet which does not require regularly scheduled maintainence or provision for regular access into the interior of the compressor/separator installation.
A more simple, easily fabricated and inexpensive, yet highly reliable and efficient liquid-gas separator is required which removes a predetermined amount of oil from the oil gas mixture discharged by a screw compressor in a refrigeration application.